1. Field of the Invention
The present invention concerns a laminate board which is applicable to the manufacture of a printed circuit board and a process for continuous molding of a plate for use in producing the laminate board.
2. Description of the Prior Art
It is well-known that a material having a low dielectric constant (Er) and dissipation factor (tan .delta.) is advantageous for use in printed circuit boards. As the dielectric constant goes down, the electric performance, as measured by time delay, capacitance, and other factors, is improved.
Many materials having a low dielectric constant, such as polyethylene, poly 4-methyl pentene-1, polystyrene, polytetrafluoroethylene are not necessarily suitable for use in printed circuit boards from the viewpoints of heat resistance, cost or processability.
Incorporation of a filler into a resin is a well-known technique for improving properties of the resin such as electric, optical, mechanical, electromagnetic, frictional, chemical and other properties.
One method for lowering the dielectric constant of a material is to incorporate a filler such as one consisting of hollow microspheres, as disclosed in Japanese Patent Publication No. 18353/82 (Tokko-sho No. 57-18353); and F. W. Haining & D. G. Herbaugh, IBM TECH. DISCLOSURE BULL (USA) Vol. 22. No. 5, 1799, October 1979. The glass epoxy laminates prepared by conventional processes according to the above method using epoxy/microsphere prepregs, however, do not necessarily perform well in a printed circuit board. For example, the board's deviation from flatness, such as bending and twisting causes problems in subsequent treatments such as soldering, etching, drilling, laminating of resist, and plating. These defects may be due to uneven distribution of the filler in the prepregs. Furthermore, the electrical insulation of the board is not as large as is required when the board is immersed in boiling water. Voids formed between the filler and the reinforcing fabric are considered responsible for these disadvantages.